Method for, and a topology aware resource manager in an ip-telephony system

ABSTRACT

The present invention relates to a method and arrangement in a communications network. The object of the present invention is to provide a way of handling recourse management issues and admission control within an IP telephony system. The object is achieved by a topology aware resource manager collecting routing information concerning the IP network, obtaining resource information concerning resources within the IP network, creating a resource map by means of combing said routing information and resource information, and performing recourse management issues and admission control within the system by means of said resource map and by interacting with a gatekeeper.

[0001] The present invention relates to a method and arrangement in acommunications network in accordance with the preambles of theindependent claims. More specifically it relates to IP telephonyrecourse management issues and admission control within an IP telephonysystem.

BACKGROUND OF THE INVENTION

[0002] Telephony is one of the most important inventions in mankind.Since its birth Mar. 10:th, 1876, installing copper wires to each andeveryone that needed communication capabilities has spread thetechnology worldwide. By coupling copper wires together between callerand called, a connection between these was achieved and they couldeventually communicate with each other through their circuit. This kindof technology has become known as circuit-switched telephony. Anyonefamiliar with classical telephony know that there has been a greatevolution within this circuit-switched telephony with, for instance, theAXE platform the Ericsson Corporation developed as their switchingsolutions. Knowledge about statistical multiplexing of calls within thenetworks has make it possible to build networks with worldwide coverageto limited costs.

[0003] During the last decade, the classical circuit-switched telephonyservice has met a competitor in the more cost efficient packet-switchedtelephony built upon the Internet protocol suite Transport ControlProtocol/Internet Protocol (TCP)/(IP). This telephony is usuallyreferred to as IP telephony, which currently is being standardized andfrequently installed instead of the old circuit-switched telephony.

[0004] The packet-switched IP telephony networks are commonly routedusing one of the well-known IP routing protocols such as OSPF (Moy J.,OSPF Version 2, IETF, RFC2328), IS-IS (Oran D., OSI IS-IS Intra-domainRouting Protocol, IETF, RFC1142) or RIP (Malkin G., RIP Version 2, IETF,RFC2453). These protocols can be classified either as being link-stateor distance vector protocols based on the algorithms they use for routecomputation and distribution of routing information. All routers runninga link state protocol within a domain have a complete view of thenetwork, knowing all the networks and routers within the domain. Adistance vector router knows only the routers and networks in itsimmediate surrounding (directly connected).

[0005] Most commercial IP telephony systems follow the InternationalTelecommunication Union-Telephony (ITU-T) Recommendation H.323. Thisrecommendation was early adopted by major IP telephony vendors in theirsystems solutions. In FIG. 1, an overview of the major components in anH.323 system is shown.

[0006] These major components are terminals T, gateways G, andgatekeepers Gk. The three first components are referred to as endpointsof the H.323 system since these can initiate or terminate media streams.The gatekeeper is the manager of the H.323 system. The managing domainis referred to as a zone. There is one, and only one, gatekeeperavailable in each zone.

[0007] Terminals

[0008] Terminals T are endpoints that provide real-time two-waycommunications, i.e. it is possible to talk and listen to another H.323terminal T or another telecommunications system via a gateway. It canalso participate in a multipoint conference through the MCU, which willbe introduced below. An H.323 terminal T must support the voice service.Besides the voice service, the terminal T con also provide video anddata services, but these are optional. To be able to negotiate channelusage and do capability exchange between end-points, the terminal T mustalso support H.245. Other required components are call setup andsignalling via Q.931, registration/admission/status (RAS) for gatekeepercommunication, and RTP/RTCP for transportation of real-time services,e.g. voice and video.

[0009] Besides these required components, the terminal T could also haveMCU capabilities.

[0010] Gateway

[0011] A gateway G is an interface between an H.323 system and anothertelecommunication systems, e.g. PSTN. The gateway G is optional and isonly required when an endpoint communicates with other terminal types102, e.g. ISDN, PSTN etc. The gateway G handles both the call controland the call transportation translation between the H.323 system and thenon-H.323 system.

[0012] Multipoint Control Units

[0013] The multipoint control units (MCU) support conferences betweenthree or more endpoints. The MCU comprises a mandatory multipointcontroller (MC) and optionally one or more multipoint processors (MP).The MC can be co-located with another end-point, e.g. in a terminal. TheMC handles negotiations between terminals during audio and videocapability exchange. The MC also determines if any of the related mediastreams should be distributed with multicast. In case mixing of mediastreams are required, the MP handles this. As depicted in FIG. 2,Multipoint communication can be made either in a centralised or adecentralised manner. In centralised multipoint conferencing, allcommunication between endpoints E is made via the MC. In the MC, themedia streams are mixed together and distributed to involved endpointsE. In decentralised multipoint conferencing, the MC handles thenegotiations while the endpoints E them self distributes the mediastreams. This distribution can be made with the resource efficienttechnology multicast. A mesh of unicast media distribution can also beused. Besides the centralised and the decentralised distributionmethods, hybrids between these are possible.

[0014] Gatekeeper

[0015] The gatekeeper Gk is the most important component of an H.323enabled network. It performs two important call control functions;address translation and bandwidth management. Address translation meansthat the gatekeeper Gk translates from aliases for terminals andgateways to IP addresses. The bandwidth management implementation isvendor specific A commonly used method is to specify a threshold for thenumber of simultaneous calls that can be made within the zone thegatekeeper Gk manages. Other methods might exist but these are in thatcase vendor specific. Calls can be made directly between endpoints orvia the gatekeeper Gk. The latter is referred to as gatekeeper-routedcalls.

[0016] Even though H.323 primarily was developed for non-guaranteedquality of service networks, the recommendation has been expanded tocover Quality of Service (QoS) issues as well. For instance, QoS Supportfor H.323 using RSVP is discussed in appendix II of ITU-T RecommendationH.323 version 2, Packet-based multimedia communication systems, Gonova,1997.

[0017] Lack of topology awareness and path sensitive admission controlis the most important drawback of current implementations of H.323gatekeepers. In FIG. 3, a topology for an H.323 enabled network 300 isshown. In the network there are three edge routers ER, one gatekeeper Gkand one gateway G to PSTN. In this network the routers R that connectsLAN segments are geographically distributed, e.g. Stockholm, Gothenburg,Malmo, etc. Between these geographically distributed routers R thebandwidth is limited. The gatekeeper Gk manages the whole network whichthen defines a zone. The gatekeeper Gk and the gateway G aregeographically located where the number of users is highest. Thegatekeeper GK could be located anywhere, but for practical reasons theseare co-located. The logical location for the gateway G is to place itwhere most of the calls are made. This will result in less routing ofcalls through the rest of the network, which would be the case if thegateway G were located in a LAN segment far away from the majority ofthe users.

[0018] The gatekeeper Gk can be configured to allow X simultaneous callson a heuristic basis. If the perceived quality is degraded, thethreshold of simultaneous calls can be decreased. This heuristicdecision base will cause problems. One user can, with or withoutmalicious intentions, cause low overall utilisation and denial ofservice to other users. By starting sessions that use a thin bottlenecklink, the heutistics will be adjusted to allow very few sessions in thezone. Other users that are connected with well-provisioned links willthen be denied access, even if the bottleneck link would not be involvedin those sessions. Other problems will occur when the usage behaviour ischanged in some way, or when there are topology changes. Changed userbehaviour could be that more users than usually gets their calls routedover a thin or loaded link, which could cause packet drops or increaseddelays. Topology change could be caused by link failure. This causesrerouting of packets meaning that the packets then take alternate pathsthrough the network. Topology change can also be that a linkcharacteristic is changed in some way, e.g. increased or decreasedbandwidth, delay, etc.

[0019] Another problem is that gatekeeper-routed calls connot beguaranteed high service quality in case direct calls are allowed. If agatekeeper Gk performs bandwidth management for gatekeeper-routed callsin a zone and is unaware of simultaneous direct calls, the total trafficvolume may exceed available bandwidth at some link. The problem here isthat both gatekeeper-routed and direct calls use the same resources.This is due to that the gatekeeper Gk performs bandwidth management andapproves bandwidth requests on gatekeeper-routed calls while directcalls can be made within the network without informing the gatekeeperabout the bandwidth usage. In the case where direct calls are usedwithin the IP telephony network, service differentiation, i.e.mechanisms in network elements that prioritise and forward importantcalls before less important calls, is necessary as soon as some sort ofguarantees for a service is required. Gatekeeper approved calls can thenbe marked as important and forwarded first while direct calls are markedas less important.

[0020] For ongoing calls, problems might occur if there are additionalendpoints that want to join the session and these endpoints are locatedon networks segments without available resouces or where the availableresources are not sufficient to provide predictable service. This issuewill only occur when there is a multipart conference involving more thantwo endpoints.

[0021] Yet another problem is that different H.323 zones might beseparated by non-H.323 enabled networks. Currently there are no means toprovide a predictable service in this case because resources are notcontrolled in a non-H.323 network.

[0022] QoS support for H.323 using RSVP is currently under development.However, QoS support using RSVP is not scalable, especially not whenthere are calls made between endpoints in different zones where thereare a non-H.323 enabled network in between. RSVP does per callsignalling and reservations that would load the networks with signallinginstead of useful traffic, i.e. media streams, and set-up per call statein routers.

[0023] Current H.323 systems do not allow reservations in advance, whichmakes it hard to plan meetings with predicted quality.

[0024] Yet another problem in the H.323 standard is that a bandwidthrequest is always approved or rejected. A more flexible approach betweenthe bandwidth management functionality and the end-user is preferred.

[0025] The European patent document EP 0942560 discloses an apparatusand method for speech transport with adaptive packet size. It aims tominimize end-to-end delays caused by network traffic and low capacityrouters in the network topology between two IP telephony devises. Theaim is achieved by adopting packet sizes for speech transport. However,the document do not address how admission control can be done in speechtransport systems, i.e. evaluating if there are sufficient capacity inthe network before staring sessions and for communicating admissiondecisions to the system.

SUMMARY OF THE INVENTION

[0026] The object of the present invention is to provide a way ofhandling recourse management issues and admission control within an IPtelephony system.

[0027] The above-mentioned object is achieved by a method, a resourcemanager and a system according to the characterising part of theindependent claims.

[0028] Thanks to that the topology aware resource manager provided bythe present invention, comprises means for collecting routinginformation concerning the IP network, means for obtaining resourceinformation concerning resources within the IP network, means forcreating a resource map by means of combing said routing information andresource information, and means for interacting with the gatekeeper itis possible for the resource manager to perform recourse managementissues and admission control within the system.

[0029] The method provided by the present invention comprising the stepsof:

[0030] collecting routing information concerning the IP network;

[0031] obtaining resource information concerning resources within the IPnetwork;

[0032] creating a resource map by means of combing said routinginformation and resource information;

[0033] makes it possible to perform recourse management issues andadmission control within the system, by means of said resource map andby interacting with a gatekeeper.

[0034] Preferred embodiments are set force in the dependent claims.

[0035] An advantage of the present invention is that increasedutilisation of the network that will be achieved.

[0036] Another advantage of the present invention is that it is bepossible to prioritise certain traffic and still allow other traffic inthe same network. This gives flexible system solutions.

[0037] Another advantage of the present invention is that it makes itpossible to reserve resources in advance to allow planned meetings andevents.

[0038] Yet another advantage of the present invention is that it makesit possible to allow calls with predictable quality through non-H.323domains if these domains where QoS enabled with inter-domaincommunicative resource managers. It would be In these inter-zonessegments resources can be reserved in advance for traffic aggregates toavoid per call signalling in these segments, i.e. trunk bandwidth. Thisis a very resource efficient feature of the described technology.Reservations in advance are allowed to vary over time, e.g. reserve morebandwidth during working hours and less otherwise. In other words, theuser of the described technology can schedule resources by predictingthe resource need over time.

[0039] A further advantage of the present invention is the flexibleinteraction between service provider and end-user that a full resourcemap can provide if this is a customer need.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1-3 are related to the state of the art and are describedabove.

[0041]FIG. 1 shows an overview of the major components in an H.323system according to the state of the art.

[0042]FIG. 2 is a diagram depicting multipoint communication accordingto the state of the art.

[0043]FIG. 3 is a block diagram illustrating a topology for an H.323enabled network according to the state of the art.

[0044]FIG. 4 is a block diagram illustrating an exemplary topology awareresource manager entity RM within an IP telephony system, according to afirst embodiment of the present invention.

[0045]FIG. 5 is a block diagram illustrating an exemplary topology awareresource manager entity RM within an IP telephony system 500, accordingto a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0046]FIG. 4 is a block diagram illustrating an exemplary topology awareresource manager entity RM within an IP telephony system 400, accordingto a first embodiment of the present invention. The resource manager RMcomprises topology aware resource manager functionality. It is comprisedin an IP telephony system e.g. an H.323 system. Such a system isdescribed FIG. 1, above under “background of the invention”. Hence, inaddition to the resource manager RM, the IP telephony system typicallycomprises IP telephony components such as one or many gatekeepers Gk,gateways G, and terminals, as well as IP network elements such asrouters R, edge routers ER and Local Area Network (LAN) segments towhich the terminals typically are connectable. The IP telephony system(400) is used to enables end-users to use an IP network as thetransmission medium for multimedia.

[0047] The resource manager RM interacts with the gatekeeper Gk andhandles all resource management issues for initiated and ongoing callsand admission control for call set-up requests. The interaction betweenthe RM and the Gk can be implemented in a number of ways, e.g. via acommunication protocol, inter process communication, functional callsbetween integrated software modules, etc.

[0048] Topology awareness is the availability of correct routing andresource information, which is essential to a system which performsresource management and admission control. The resource manager RMretrieves routing information concerning the IP network, i.e. thetopology of the IP network.

[0049] In the case wherein the IP network is routed using link-staterouting protocol, the resource manager RM participates in the routingand acts as a router, i.e. the RM peers with other routers, withoutadvertising any routers of its own, to retrieve routing information ofthe IP network. The basic principle on which link-state protocols arebuilt ensures that all routers have the complete routing information.When participating in the routing protocol, the resources manager RMreceives the routing information as fast as any other router in therouting domain and can therefore detect changes in the topologyinstantly.

[0050] In the case wherein the IP network is routed using a distancevector protocol, or static routing, the method of peering cannot beused. In this case, the routing information is retrieved by measurementssuch as trace route (See Kessler G., A Primer on Internet and TCP/IPTools, IETF, RFC1739) and/or the use of Simple Network ManagementProtocol (SNMP) auto discovery (see Kesbav et Al, Discovering InternetTopology,

[0051] http;//www.cs.cornell.edu/skesbav/papers/discovery.pdf, July1998). SNMP is a set of protocols for managing complex networks. Whenthe resource manager RM has retrieved the routing information, it uses anetwork management protocol, such as SNMP (see Case et Al, Introductionto Version 3 of the Internet-standards Network Management Framework,IETF, RFC2570), to collect information on the routers and theirinterfaces (e.g. the interface type and speeds). The information is usedby the RM to complement the gained routing information and make surethat it has an accurate routing topology. The resource manager RMcombines the routing information and resource information it gets fromcall set-up requests from the Gk to create a resource map. The resourcemap contains information of how much resources (e.g. bandwidth) that areavailable and reserved over time on a per link basis. The resourcemanager RM uses the resource map to assist the gatekeeper Gk in thedecision whether there are resources available or not, for a call thatsomeone is initiating.

[0052] In the case of gatekeeper-routed calls, the gatekeeper Gk isresponsible for approving or rejecting initiated calls from terminals.The gatekeeper Gk interacts with the resource manager RM and asks theresource manager RM if there will be enough resources through the routedpath between the source endpoint and the destination endpoint of aninitiated call, to give the predictable quality. The resource manager RManswers the question by evaluating what network path the call will useand for each link along that path it calculates if there are sufficientresources to admit the call, i.e. the resource manager RM performspath-sensitive admission control on the resource request. The admissioncontrol is performed based on the information in the resource map. Thiswill solve the above-mentioned problem addressed as the changes in userbehaviour. No heuristic model can cope with changes in user behaviour,but the topology aware resource manager RM does that by being up to dateabout the resource utilisation. The same goes for the problem withdenial of service.

[0053] Another problem addressed above is the changes in topology. Theresource manager RM monitors on-going calls in the IP telephony systemand recalculates the resource usage per link whenever any change occursi.e. updates the resource map. If the updated resource map show thatresources are too limited to be able to fulfil all on-going calls theresource manager RM will report this to the to the gatekeeper Gk. If theresources are limited as just described, it is possible to let eitherthe resource manager RM or the gatekeeper Gk prioritise which calls thatshould be kept and which to terminate. BY performing thisprioritisation, degraded quality for everyone involved is avoided. Thisprioritisation also makes the number of lost calls minimised. Anotherway to prioritise services whenever topology changes occur is to letvideo streams gets lower priority compared to the voice service.

[0054]FIG. 5 is a block diagram illustrating an exemplary topology awareresource manager entity RM within an IP telephony system 500, accordingto a second embodiment of the present invention. In this secondembodiment, the resource manager RM is used in a multipart conferencingscenario involving more than two endpoints. Within a multipartconferencing there will always be a multipoint controller MC involved inthe communication. The IP telephony system shown in FIG. 5 is the sametypically IP telephony system as the one in illustrated in FIG. 4 exceptfor that it additionally comprises a multi-point controller MC. Thesystem may comprise more than one multi-point controller. Themulti-point controller MC has knowledge about which endpoints thatparticipates in the multipart conference and the MC will also controlthese endpoints. The resource manager RM provides the admission controlto the multi-point controller MC, either directly or indirectly via thegatekeeper Gk, in the same way as provided to the Gk as describe above.The resource request may in this case contain more then two endpoints.

[0055] In a multipart conferencing call, a task to add participants asresource efficiently as possible arises. In this case, the resourcemanager RM recommends the multi-point controller MC, by means of theresource map, which distribution method (centralised/decentralised or anappropriate hybrid between these) to use to make it possible for theadded part to join the session in a resource efficient manner. Thedistribution method to use is depending on the resource map and hence,only the resource manager RM has the possibility to answer this.

[0056] In case there are no resources available with predictablequality, different methods to handle this exists. The user can getservice without priority or the user can be rejected to participate inthe conference due to lack of resources.

[0057] In case different priorities are used, there must be either twomulticast sessions of which one is prioritised and the other is not, ora separate unicast session to the part that suffers from lack ofresources.

[0058] In the multicast case, the part with less predictable resourcesmust listen to the session without priorities and the traffic willtherefore never be distributed to that part of the network.

[0059] In the unicast case, one part of the session can relay itstraffic as unicast without priority to the part with lack of predictableresources.

[0060] For both the unicast case and the multicast case, the bandwidthrequest is approved or rejected. From an end-user point of view it ismore convenient to have a reject with conditions, which is possible whenusing the resource manager RM according to the present invention.

[0061] For instance, the end-user requests for 64 kbit/s voice serviceand 128 kbit/s video service. The available resources are not sufficientto fulfil this request but only 128 kbit/s is available which is foundout by the resource manager RM by means of the resource map. The answerfrom the resource manager RM could then be e.g. “Your request cannot befulfilled, only 128 kbit/s can be reserved for you. Please respond tothis message within 5 minutes to reserve these 128 kbit/s.” Apreliminary booking of resources is made by the resource manager RM,based on the original request from the gatekeeper Gk or multi-pointcontroller MC. This preliminary booking request is then cancelled unlessthere is a response to the message sent from the resource manager RM tothe gatekeeper Gk or MC. For the end-user, it is then possible to selectwhich service to prioritise in favour of the other. I.e. that is in casethere is a wish to put either of the services in favour of the other.The same goes if only one service is considered. The user wants e.g. torun high-quality voice, but due to lack of resources he acceptsmedium-quality voice with predictable quality rather than high-qualityvoice without possibilities to predict the quality.

[0062] Even though the state of the art describes H.323 and the solutionaccording to the present invention is adapted to that recommendationother similar IP telephony solutions are possible, e.g. there exists acompeting IP telephony solution according to the IETF standard SIP wherethe same solutions are applicable.

[0063] The resource manager RM comprises means for performing themethods steps described above.

[0064] The resource manager functionality is implemented by means of acomputer program product comprising the software code means forperforming functionality. The computer program is run on a standaloneserver interacting with gatekeepers, or is run on the same hardware asthe gatekeeper functionality. It can be integrated with software thatimplements gatekeeper functionality, it may also run on routers or othernetwork entities. The resource manager functionality may also bedistributed to run on multiple nodes and/or distributed geographicallyover a network. The above is also applicable for interaction with otherentities performing the same functionality as gatekeepers. The computerprogram is loaded directly or from a computer usable medium, such as afloppy disc, a CD, the Internet etc.

[0065] The present invention is not limited to the above-describedpreferred embodiments. Various alternatives, modifications andequivalents may be used. Therefore, the above embodiments should not betaken as limiting the scope of the invention, which is defined by theappending claims.

1. A topology aware resource manager (RM) within an Internet Protocol IPtelephony system (400) for transmission of multimedia over an IPnetwork, the system comprising a gatekeeper (Gk), wherein the resourcemanager (RM) comprises: means for collecting routing informationconcerning the IP network; means for obtaining resource informationconcerning resources within the IP network; means for creating aresource map by means of combing said routing information and resourceinformation; characterised in that the resource manager (RM) comprises:means for via the gatekeeper (Gk) performing path sensitive recoursemanagement issues and admission control within the system (400) by meansof said resource map and by interacting with the gatekeeper (Gk).
 2. Theresource manager (RM) according to claim 2, wherein it comprises meansfor obtaining resource information from call set-up requests from thegatekeeper (Gk).
 3. The resource manager (RM) according to any of theprevious claims 1-2, wherein the IP system is routed using link-staterouting protocol, the resource manager (RM) comprises means forparticipating in the routing and acting as a router within the system(400) without advertising any routes of own, to retrieve routinginformation of the IP network.
 4. The resource manager (RM) according toany of the previous claims 1-2, wherein the IP network is routed using adistance vector protocol, or static routing, the resource manager (RM)comprises means for using measurements such as trace route and/or theSimple Network Management Protocol (SNMP) auto discovery to retrieverouting information of the IP network.
 5. The resource manager (RM)according to any of the previous claims 1-4, wherein it comprises meansfor using the resource map for evaluating what network path an initiatedcall between a source endpoint and a destination endpoint within thesystem (400) will use.
 6. The resource manager (RM) according to claim5, wherein it comprises means for, calculating, for each link along thatpath, if these are sufficient resources to admit the call.
 7. Theresource manager (RM) according to claim 6, wherein said calculation isreported to the gatekeeper (Gk).
 8. The resource manager (RM) accordingto any of the previous claims 1-7, wherein it comprises means forupdating the resource map by monitoring on-going calls in the IPtelephony system and recalculating the resource usage per link wheneverany change occurs within the system (400).
 9. The resource manager (RM)according to claim 8, wherein the resource map shows that the resourcesare too limited to be able to fulfil all on-going calls, the recoursemanager (RM) comprises means for prioritising which calls that should bekept and which to terminate.
 10. The resource manager (RM) according toclaim 8, wherein the resource map shows that the resources are toolimited to be able to fulfil all on-going calls, the recourse manager(RM) comprises means for reporting this to the gatekeeper (Gk), makingit possible for the gatekeeper (Gk) to prioritise which calls thatshould be kept and which to terminate.
 11. The resource manager (RM)according to any of the previous claims 1-10, wherein it is used in amulti part conference scenario involving more than two end-points withinthe system (500) which system further comprises a multi-point controller(MC), the resource manager (RM) comprising means for interacting withthe multi-point controller (MC) for performing said recourse managementissues and admission control.
 12. The resource manager (RM) according toclaim 11, wherein said interaction with the multi-point controller (MC)is performed via the gatekeeper (Gk).
 13. The resource manager (RM)according to any of the claims 11-12, wherein recourses are available,but not enough to fulfil the amount of recourses requested in a callinitiation, the resource manager (RM) comprises means to reject the callwith conditions, i.e. by offering said available recourses to theinitiator of the call.
 14. An Internet Protocol (IP) telephony systemcomprising a gatekeeper (Gk), one or more routers (R) and multiple aplurality of end-points characterised in that the system furthercomprises a topology aware resource manager (RM) according to any of theclaims 1-13.
 15. A method for handling performing recourse managementissues and admission control within an Internet Protocol IP telephonysystem (400) adapted for transmission of multimedia over an IP network,the system (400) comprising a topology aware resource manager (RM);characterised in that the method comprises the following steps to beperformed by the resource manager (RM). collecting routing informationconcerning the IP network; obtaining resource information concerningresources within the IP network; creating a resource map by means ofcombing said routing information and resource information; via thegatekeeper (Gk) performing path-sensitive recourse management issues andadmission control within the system (400) by means of said resource mapand by interacting with a gatekeeper (Gk).
 16. The method according toclaim 15, comprising the further step of the resource manager (RM)obtaining resource information from call set-up requests from thegatekeeper (Gk).
 17. The method according to any of the claims 15-16,wherein the IP system is routed using link-state routing protocol, themethod comprising the further step of: the resource manager (RM)participating in the routing and acting as a router within the system(400) without advertising any rotes of its own, to retrieve routinginformation of the IP network.
 18. The method according to any of theclaims 15-16, wherein the IP network is routed using a distance vectorprotocol, the method comprising the further step of: the resourcemanager (RM) using measurements such as trace route and/or the SimpleNetwork Management Protocol (SNMP) auto discovery to retrieve routinginformation of the IP network.
 19. The method according to any of theclaims 15-18, comprising the further step of: using the resource map forevaluating what network path an initiated call between a source endpointand a destination endpoint within the system (400) will use
 20. Themethod according to any of the claims 15-19, comprising the further stepof: calculating for each link along that path, if there are sufficientresources to admit the call.
 21. The method according to claim 20,comprising the further step of: reporting said calculation to thegatekeeper (Gk).
 22. The method according to any of the claims 15-21,comprising the further step of: the resource manager (RM) updating theresource map by monitoring on-going calls in the IP telephony system andrecalculating the resource usage per link whenever any change occurswithin the system (400).
 23. The method according to claim 22, whereinthe resource map shows that the resources are too limited to be able tofulfil all on-going calls, the method comprising the further step of:the resource manager (RM) prioritising which calls that should be keptand which to terminate.
 24. The method according to claim 22, whereinthe resource map shows that the resources are too limited to be able tofulfil all on-going calls, the method comprising the further step of:the resource manager (RM) reporting this to the gatekeeper (Gk), makingit possible for the gatekeeper (Gk) to prioritise which calls thatshould be kept and which to terminate.
 25. The method according to anyof the claims 15-24, wherein it is used in a multi part conferencescenario involving more than two end-points within the system (500),which system further comprises a multi-point controller (MC), themethods comprising the further step of: the resource manager (RM)interacting with the multi-point controller (MC) for performing saidrecourse management issues and admission control.
 26. The methodaccording to claim 25, wherein said interaction with the multi-pointcontroller (MC) is performed via the gatekeeper (Gk).
 27. The methodaccording to any of the claims 25-26, wherein recourses are available,but not enough to fulfil the amount of recourses requested in a callinitiation, the method comprising the further step of: the resourcemanager (RM) rejecting the call with conditions, i.e. by offering saidavailable recourses to the initiator of the call.
 28. A computer programproduct directly loadable into the internal memory of a processing meanswithin a topology aware resource manager (RM) and/or a gatekeeper (Gk)within a IP telephony system (400) system, comprising the software codemeans for performing the steps of any claims 15-27.
 29. A computerprogram product stored on a computer usable medium, comprising readableprogram for causing a processing means in topology aware resourcemanager (RM) and/or a gatekeeper (Gk) within a IP telephony system (400)system, to control an execution of the steps of any of the claims 15-27.